1. Field of the Invention
This invention relates to telephone subscriber alerting systems and, more particularly, to the transmission of digital busy signals when all paths through a digital switching or transmission system are busy.
2. Description of the Prior Art
With the advent of automatic telephone dialing it has become common practice to return a fast-busy tone to the calling party when all paths through a central office or when all trunks are in use. Auxiliary equipment is normally required to generate and transmit such a fast-busy tone to a calling party. In more recent times, central offices utilize digital samples, which are stored, for example, in a read only memory (ROM) are transmitted to a digital-to-analog converter. The output signal from the converter is then transmitted to the calling party as the fast-busy stone. One such tone generator is disclosed in U.S. Pat. No. 4,171,466 granted to Mr. Robert L. Carbrey.
In a digital concentrator system such as the one disclosed by applicant in his copending application, Ser. No. 186,619, filed of even date herewith, it is likewise desirable to return a fast-busy signal to a calling party when all concentrator trunks are in use, however, without the use of auxiliary equipment.